Prior art employs round diaphragms of thin material used to isolate pressure instruments from harmful conditions. The diaphragm becomes a mechanical barrier between the process fluids and a liquid which transmits the pressure to the pressure instrument. The diaphragm must have flexibility to displace sufficient fill liquid to allow the instrument to perform its pressure measurement function and should not impose a detrimental pressure drop during the displacement. Shortcomings of such an instrument are that the diaphragm size places limitations on the instrument sensitivity. The thickness of diaphragm materials such as metal foil and the volumetric displacement versus pressure loss also present disadvantages. Round diaphragms are mostly used with pressure gauges such as bourdon tube types that have very small volumetric displacements. For example, a diaphragm of 1.4 inches diameter 0.003 inches thick with a volumetric displacement of 0.025 cubic inches will easily operate bourdon gauges or force balance instruments or other similar devices. But for instruments that utilize bellows to measure pressures, flows or tank levels the displacement requirements necessitate large diaphragms such as 4 inches in diameter and for installation the large diaphragm requires large flanges or apertures in process vessels or piping.
The present invention overcomes the size displacement limitations of the round metal diaphragm. A new rectangular design or at least oval can have the installation dimensions of a small round diaphragm with the volumetric displacements of a large round diaphragm. Also the design has capabilities of various displacements. The probe aspect of the seal also provides deeper penetration into a vessel preventing build up a contaminants on flush diaphragms.